can you help me to understand that in on page optimization while choosing keyword if i have too keyword one having Hugh number of search result and other having very small number of search result in Google adword then which one to use?

To use keyword you can use the keyword tool to find the keywords that you want to keep in way of. A keyword is a word that is a topic of importance to your company. After adding the keyword in the tool you will use that on your website pages and visitors can use that keyword for their searches.

I recommend you to choose keyword with less searches, It would be easy to rank less competitive keywords, as you will be able to rank highly searched keyword relatively easy after ranking first keyword with less searches..